Mowing blade with star

ABSTRACT

A shape for the central drive hole of a rotary mowing blade, such shape including two pairs of teeth extending off of a central hole substantially displaced 30° from the central axis of the mowing blade.

This application is a continuation of Ser. No. 08/755,627, filed on Nov.25, 1996, which is now U.S. Pat. No. 5,724,796. U.S. Pat. No. 5,724,796is a continuation of Ser. No. 08/130,713, which was filed on Oct. 4,1993, and is now abandoned.

FIELD OF THE INVENTION

This invention relates to a mowing blade using an asymmetrical star fora power passing interconnection with a rotating blade spindle.

BACKGROUND OF THE INVENTION

For many years, lawn mower blades were simply bolted on to the bottom ofa rotating shaft. As the blades themselves were a little more thanstraight pieces of sharpened stamped steel, and as all of the forces onthe blade were unidirectional, this method of interconnection workedquite well.

When the requirements for passing torque between the blade and shaftbecame bidirectional, as with the addition of a blade brake to theinterconnection, and as the blades themselves began to require greatertorque, for example mulching blades having integral fans and recuttingsections, the simple bolt no longer sufficed. Manufacturers, therefore,adapted any one of many varying techniques in order to physicallyconnect the blade normally to some sort of adapter between the blade andthe shaft. These included adapters having pins spaced from therotational axis of the shaft as well as star shaped holes in the bladewith corresponding keys on the shaft.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide for a reliable meansof passing bidirectional torque between a blade and a shaft.

It is another object of the present invention to increase the longevityof the interconnection between a blade and shaft.

It is yet another object of the present invention to reduce the cost ofan interconnection between a blade and shaft.

It is still another object of the present invention to reduce thecomplexity of the interconnection between a blade and a shaft.

Is is a further object of the present invention to simplify themanufacture of an interconnection between a blade and a shaft.

Other objects and a more complete understanding of the invention may behad by referring to the following description and drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation, and advantages of the presently disclosedpreferred embodiment of the invention will become apparent whenconsideration of the following description taken in conjunction with theaccompanying drawings wherein:

FIG. 1 is a downward view of the center section of a rotary bladeincorporating the invention of the application;

FIG. 2 is an enlarged upward view of the adapter to be utilized with therotating shaft and the blade of FIG. 1;

FIG. 3 is a lateral cross sectional view of the adapter of FIG. 2 takenapproximately along lines 2—2 thereof. The figure also includes theblade bell support; and,

FIG. 4 is a downward view of the blade bell support of FIG. 3 inconjunction with a central sideward cross sectional view thereof.

FIG. 5 is a cross-sectional view of the blade bell support as takenalong 5—5 of FIG.4.

DETAILED DESCRIPTION OF THE INVENTION

The interconnection of this invention is designed for use with a rotarylawn mower. The rotary lawn mower, which may be single or multiplespindle, includes a shaft 10, a blade adapter 20, a blade bell support50, and a blade 70.

The spindle 10 is a round shaft that is supported by a bearing assembly(not shown) to a mower deck (also not shown). This shaft, which may beintegral with the engine shaft, or which may exist singularly or inspaced multiples, is driven by an engine, normally through some sort ofclutch/brake assembly. When the shaft is being rotated by the engine orengine shaft, the torque is passing in one direction from the shaft 10to the blade 70. When the shaft 10 is braked or otherwise being slowedrelative to the blade 70, the torque passes in the opposite directionbetween the blade 70 and the shaft 10. The torque is thus passedbidirectionally between the shaft 10 and blade 70. The particular shaftdisclosed has a threaded hole 11 and a generally rectangular key way 12formed at its lower end. These are used to interconnect the shaft 10 tothe blade adapter 20 as later described. Other means could also be used.

The blade adapter 20 physically interconnects the shaft 10 to the blade70 in order to pass bidirectional torque therebetween. The particularadapter disclosed is designed for use with the rotary shaft 10 havingthe threaded hole 11 and the rectangular key way 12 previouslydescribed. This adapter 20 includes a mounting section 21, a flangesection 22, and a star section 23. This blade adapter is preferablyconstructed of powder metal. It could also be integral with the shaft10.

The mounting section 21 includes a circular hole 25 extendingtherethrough. The cross sectional shape and diameter of this hole 25 isselected to match the cross sectional shape and diameter of the shaft 10to be utilized with such blade adapter. The particular hole disclosed isthus round with a rectangular key 26 matching generally the shape of thekey way 12 on the shaft extending therein. The depth of the hole 25 isselected so as to solidly interconnect the blade adapter 20 to the shaft10. This is particularly important in respect to angular wobbling due tothe high forces which are generated between the shaft 10 and the blade70. The thickness of the walls of the mounting section 21 are designedwith similar thoughts in mind. In the particular embodiment disclosed,the diameter of the hole is approximately 0.875″ in diameter with thekey way extending approximately 0.075″ therein, such key way having awidth of approximately 0.1837″. The height of the mounting section 20 isapproximately 0.80″ with a wall thickness of 0.250″.

The flange section 22 serves to mechanically interconnect the mountingsection 21 with the star section 23 as well as providing an increasedangular support for the blade 70.

The central section 30 of the flange section 22 between the star section23 and the walls of the mounting section 21 passes the torquebidirectionally therebetween.

The remainder of the flange section 22 serves as a physical support forthe blade. Theoretically, this support section should be as large aspossible within the physical dimensions of the available matchingsection of the blade. Such a size would, however, cause a parasiticpower loss due to the cross sectional height of this support section 31as well as potentially compromising the airflows under the mowing deckcaused by the blade. The physical dimensions of the support section aretherefore chosen in an optimization procedure to provide the necessaryangular support for the mower blade while at the same time not undulycompromising the below deck air flow. In the particular embodimentdisclosed, the support section is a generally rectangular member havinga flat bottom surface 32. This flat bottom surface 32 is selected with alength and a width to match the angular deflection requirements of theblade 70 being utilized with such point adapter 20. As the particularblade 70 is a mulching blade, the matching flat surface on the blade isof a certain distance between the downward extending rounded edgesection. This width is slightly less than if the blade width 70 was aconventional discharge blade. The bottom surface 32 of the blade adapterhas a width selected to match this flat surface width of the blade 70,thus optimizing the support for torsional bending of the blade (i.e.,any further increase in width would not serve to support the blade anyfurther). As width does not generally compromise air flow, this widthcan be preferably maximized. The width of the blade is selected in anoptimization of this need for torsional support. The length of thebottom surface of the blade adapter 20 is designed to minimize an up anddown flexing along the length of the mower blade 70. Ideally, toaccomplish this purpose, the length would match the length of the flatsurface of the blade 70, thus optimizing this functioning. However, sucha length would, as previously discussed, potentially compromise the airflow under the mower deck as well as producing parasitic power lossesdue to an increased cross sectional area. The length is thus chosen inan optimization procedure to provide a sufficient longitudinal angularflexing support for the blade while at the same time minimizingparasitic type losses. In the embodiment shown, this means the length ofthe blade adaptor 70 is approximately ⅙ of the length of the blade.

In the preferred embodiment disclosed, the support section of the bladeadapter has a width of 1.38″, a length of 3.30″ with the ends roundedwith approximately a 0.69 radius. This radiusing of the ends is designedto eliminate a point to point contact which could otherwise occur at theouter ends of the blade adapter on any flexing and/or torsional movementof the blade. Rounded corners are also easier to construct in the powdermetal construction utilized for this particular blade adapter 20. Theheight of the flange section 22 is selected in order to retain thebottom surface 32 flat in contradiction to the torsional and angularforces produced by the blade 70. Ideally, the height is selected so asto produce no flexing of the bottom surface 32 under anticipated forces.In the particular embodiment disclosed, the height is approximately0.38″. Note that with this height, the bottom of the hole 25 and themounting section 21 is located slightly above the top surface of theflange section 22. This slightly strengthens this section by providing aslight angle therebetween, thus increasing the lateral shear strengthbetween the mounting section 21 and the flange section 22.

The star section 23 of the blade adapter 20 is the main mechanicalinterconnect between the blade adapter 20 and the blade 70. Ideally,this mechanical interconnect should have a solid rotational contact withthe blade so as to optimize the torque transfer between the shaft 10 andthe blade 70. The star should therefore physically locate the bladeagainst any rotation in respect to the shaft while at the same timemaximizing the cross sectional surface area of contact between the starand blade, thus insuring the efficient passage of torque. In addition,preferably the star section would be designed so as to correctly alignthe blade 70 with the blade adapter 20 under non-skilled attachment.This would allow for the correct positioning of the two components whenserviced in the field, thus allowing the manufacturer's design to becontinued to be implemented after such servicing. In the particularembodiment disclosed, there are two equally correct positions for theblade 70 in respect to the blade adapter 20, each position 180° oppositethe other. In this particular preferred embodiment, the star section 23has a generally circular profile center section 40 with four protrudingasymmetrical teeth 41. These teeth 41 are generally in symmetricalalignment with the longitudinal length of the later described blade,thus optimizing the amount of material between such teeth and thelateral edges of the blade 70.

Central section 40 of the star section 23 primarily provides an accesshole for the later described bolt that holds the blade 70 on to theblade adapter 20. The central section 40 also provides for an increasedarea of contact 42 between the star section and the blade by displacingsame from the rotational axis thereof. This area of contact 42 increasesthe surface area of contact between the star section and the blade, thusincreasing the strength of this critical torque passing section. In theparticular embodiment disclosed, this central section 40 has a slightoutward arc in the middle point 43 of the sides of the star section.This circular area serves to more precisely locate the blade in respectto the star section than an alternate surface would such as a straightedge. The reason for this is that the tolerances for clearances for boththe central section and later described teeth can be less if rotarytolerances can be factored out as they can with the preferred shape.This shape also insures that the later described teeth 41 are theprimary means to pass the torque between the star section 23 and theblade 70.

The teeth 41 of the star section 23 serve to pass the primary torquebetween the blade adapter 20 and the blade 70. The teeth 41 in additionaid in insuring the alignment of the blade in respect to the bladeadapter. In the particular embodiment disclosed, the teeth 41 are fourin number, each angularly displaced symmetrically about the longitudinalaxis of the blade 70. With this orientation, the teeth 41 have a maximumamount of metal on the width of the blade 70 to pass torque to/from theblade 70 given the usage of four teeth. In addition, the orientation ofthe teeth 41 in this manner increases the critical width of contactalong the length of the blade 70, thus lowering the amount of forcewhich has to be passed per unit area. In the particular embodimentdisclosed, the central section 40 is approximately 0.685″ in circulardiameter 44. The teeth 41 are angled with an angle approximately 30° offthe longitudinal axis of the blade 70 and an angle 45 of approximately60° between their center lines, each tooth having a side profile angle46 of 40°. The end of each tooth 47 is approximately 0.141″ in width.Each tooth extends approximately 0.157″ off of the central section 40,with the total length 48 across opposing teeth being approximately 1″.The total height 49 of the tooth is approximately 0.147″. Due to thecircular profile of the center section 40, these teeth 41 pass thetorque between the star section 23 and the blade 70. In that the teeth41 are displaced by a maximal distance from the coextensive rotationalaxis, this maximizes torque transfer.

The blade bell support is designed to cooperate with the bottom surface32 of the blade adapter 20 to physically support the blade 70 in respectto such blade adapter 20. Due to the desire for both angular andtorsional support, it is preferred that the blade bell support cooperatewith the bottom surface 32 to hold the blade 70 near the ends of thelength of the blade adapter 20. This provides for a maximum support byoptimizing the cooperation between the blade adapter 20 and the blade70. Further, it is preferred that the contact between the ends of theblade bell support and the blade 70 be slightly inward of the ends ofthe length of the blade adaptor 20. This moves the point of flexingslightly inward of such ends thus increasing the strength of thisinterconnection. In the particular embodiment disclosed, the blade bellsupport in addition acts somewhat like a lock washer.

The particular blade bell support disclosed is a stamped metal parthaving a center section 51 and two adjoining ends 52. The center section51 of the blade bell support is a circular recessed section having auniform radius of depression. With this shape, any contact between thecenter section 51 and the blade occurs on the outer edges 54 of suchcenter section, an area near the width edges of the bottom surface 32 ofthe blade adapter 20 when the unit is assembled. This optimizes thesupport for the blade at two locations near to the practical useablewidth edges of the blade, thus optimizing support at this particularlocation. In addition, the recessed center section allows for sometolerances in respect to the height of the star section 23 of the bladeadapter versus the thickness of the later described blade 70. Further,since the bolt 60 holding the blade on to the adapter is tightened downagainst this center section, the recess allows for some slight flexingof the center section on tightening the bolt 60, thus helping to holdthe bolt 60 in position against ancillary rotational forces.

The ends 52 of the blade bell support 50 serve to press the blade 70against the longitudinal ends of the bottom surface 32 of the bladeadapter 20. To accomplish this, two support services 55 are located atthe ends of the blade bell support between the center section 51 and theouter radiused edges 56. These support surfaces 55 are preferablyflattened areas which comprise the uppermost part of the blade bellsupport. With this orientation, upon tightening the bolt 60 holding theblade and blade bell support to the blade adapter through hole 53, thesupport surface 55 are the first to contact the blade. On continuing totighten the bolt 60, the ends 52 of the support flex until the outeredges 54 of the center section 51 bottom against the blade. With thisorientation, the blade is primarily held against the bottom surface 32of the adapter 20 near the ends of the longitudinal length of suchbottom surface and secondarily held by the outer edges 54 of the centersection. This optimizes the angular support of the blade in respect tothe blade adapter. To insure the proper alignment of the blade bellsupport with the blade 70 and blade adapter 20, two small indexing bumps58 are formed in these approximate center of the support surfaces 55.These bumps cooperate with holes in the later described blade in orderto prevent the rotation of the blade bell support 50 in respect to theblade 70. (As the blade 70 is held in position by the star section ofthe blade adapter, this also locates the blade bell support 50 inrespect to such blade adapter 20). Due to the preferred radiusing of theouter edges 56 of the blade bell support, there is no solid line to linecontact between a sharp edge of the blade bell support and the blade 70at this critical location. This reduces the stress between the bladebell support and the blade at this location. Note that since the supportsurfaces 55 extend outward of the indexing bumps 58, there is a solidsupport for the blade 70 on the outside of the holes that cooperate withthese indexing bumps. As these holes are points of removal of material,this support on the outside thereof causes any flexing which does occurto occur at a location different than the holes. This reduces the strainon the blade at this critical point.

In the particular embodiment disclosed, the blade bell support has atotal length of approximately 3.48″ and a total width of some 1.35″. Thecenter section 51 of the blade bell support is radiused at approximate4″ radius, with such radius continuing towards the ends 52 forapproximately 1″. The support surfaces 55 extend for approximately 0.53″in width, with the indexing bumps 58 located approximately 1.250″ fromthe center of the center section 51. Each bump is approximately 0.245″in diameter extending approximately 0.040″ from the flat supportsurfaces 55. The outer radiused edges 56 are radiused at approximately0.12″. The hole 53 in the middle of the center section is approximately0.385″ in diameter. The ends 52 of the blade bell support areapproximately 0.60″across. The blade bell support is made out of 12gauge sheridized spring steel which has been heat treated according toSEAH 713A:44-48RC.

The blade 70 is a rotary mower mowing blade. As such it may take manydiffering lengths and forms. In the preferred embodiment disclosed, atypical mowing blade would be a mulching mowing blade such as thatdisclosed in U.S. Ser. No. 08/004,287 filed Jan. 14, 1993, MulchingBlade. With this blade, now U.S. Pat. No. 5,327,710 issued Jul. 12,1994, there is a flat section in the center of the blade, in thisparticular blade 1.5″ wide by 5.2″ long. This flat area and the centerdrive hole of this blade 70 has been adapted to incorporate theinvention of this present application. This is accomplished by theinclusion of a star hole into the center of the blade, with indexingholes being located longitudinally spaced therefrom.

The star hole 71 has a shape generally tracking the shape of the starsection 23 on the blade adapter. This star hole includes a centralsection 80 and slots 81. The center section 80 f the star hole 71matches generally the shape of the central section 40 of the star 23,the major different being that the center section 80 has a slightlylarger diameter so as to provide a clearance to snugly fit over thestar. Likewise, the shape of the slots 81 generally match the shape ofthe teeth 41, again with some size difference so as to provide foramounting clearance. Thos holes 82 are formed in the blade 7- tocooperate with the indexing bumps 589 of the blade bell support 50. Inthe preferred embodiment shown, the central section 80 has a diameter ofapproximately 0.702″. The slots 81 are angularly located along thecenterline of the blade separate 30° off of the longitudinal axis of theblade 70 and with approximately 60° between the longitudinal axis of theadjacent slots 81. The slots themselves are formed with a 40° sideprofile. The end of the slot is practically 0.148″ in width, with theslots extending approximately 0.180″ off of the center section 80. Thisprovides for a total length across opposing slots 81 of approximately1.012″. The blade has a total depth 89 of approximately 0.125″. The keyslots have at least one straight edge side profile where the straightedge side profile is angled at an angle of 15-25° in respect to thecenterline of the key slots. The shaded area 84 on the blade 70 showsthe location of the flat bottom surface 32 of the blade adaptor 20 inrespect to the blades profiling (shown with dotted lines 85). With thisdesign, the torque is passed between the star shaped section 23 and theblade 70 optimizing the strength of the interconnection while at thesame time maintaining a simplicity of this critical joint. Thismaximizes the torque passing qualities while minimizing the complexity,thus optimizing this critical joint.

Although the invention has been described in its preferred embodimentwith a certain degree of particularity, it is to be understood thatnumerous changes can be made without deviating from the invention ashereinafter claimed.

What is claimed is:
 1. An interconnection shape for a mower blade havinga bottom surface and a central drive hole for use with a rotating shafthaving a key shape with teeth, the interconnection shape comprising keyslots, said key slots extending outward off of the drive hole, said keyslots having at least one straight edge side profile, said straight edgeside profile being angled at an angle of 15-25° in respect to the centerline of the key slots, said side profile directly interconnecting theshaft to the blade passing torque therebetween respectively, a bladebell support, said blade bell support engaging the bottom surface of themower blade and means to connect said blade bell support to the rotatingshaft.
 2. The interconnection shape of claim 1 wherein the mower bladehas a top surface and characterized by the addition of a blade adaptorand means to connect said blade adaptor to the rotating shaft in contactwith the top surface of the blade.
 3. The interconnection shape of claim2 characterized in that blade bell support has a longitudinal lengthwith ends, and said ends of said length contacting the bottom surface ofthe blade to hold the top surface of such blade against said bladeadaptor.
 4. The interconnection shape of claim 3 characterized in thatsaid ends have outer edges and said outer edges of said ends beingradiused.
 5. The interconnection shape of claim 3 characterized in thatthe mower blade has holes, said blade support has bumps, and said bumpsengaging in said holes in order to prevent rotation of said blade bellsupport in respect to the mower blade.
 6. The interconnection shape ofclaim 2 characterized in that said blade bell support has a centralsection and said center section being radiused.
 7. The interconnectionshape of claim 1 characterized in that the mower blade has holes, saidblade support has bumps, and said bumps engaging said holes in order toprevent rotation of said blade bell support in respect to the mowerblade.
 8. The interconnection shape of claim 1 characterized in thatsaid blade bell support has a central section and said center sectionbeing radiused.
 9. The interconnection shape of claim 8 characterized inthat said blade adaptor has a width, said center section has a diameter,and said diameter being substantially equal to said width.
 10. Theinterconnection shape of claim 1 characterized in that said means toconnect said blade bell support to the rotating shaft is a bolt.